The present invention relates to methods of fabricating devices for holding a pair of axial ferrules of optical fiber connectors in opposing, axially aligned relation. More specifically, the invention relates to a method of forming a device having a pair of split sleeves for frictionally engaging respective ferrules of optical fiber connectors to ensure essentially exact axial alignment of the sleeves.
Several types or models of optical fiber connectors have been adopted as xe2x80x9cindustry standard,xe2x80x9d such as those commonly designated SC, FC, biconic, D4, etc. All connectors of this family include a so-called ferrule in the form of a cylindrical rod having a through, axial passageway wherein an optical fiber is positioned. It is often necessary to place the ferrules of two connectors in axial alignment with the free ends of the ferrules either in direct, mutual contact or spaced by a predetermined distance for controlled attenuation of light transmitted from the optical fiber of one ferrule to the other. The ferrules are maintained in this position by being axially inserted into respective split sleeves of a unitary body wherein the sleeves are positioned. The sleeves have inside diameters substantially equal to, or slightly less than, the outside diameters of the ferrules they are designed to hold. The two sleeves may be the of same or of different diameters. The outer diameter of the ferrules, as well as the diameter of the passageway through which the fiber extends and the concentricity of these diameters, is maintained within strict tolerances. However, transmission of the light beam (commonly 9mu) is unacceptably degraded if the axes of the split sleeves which hold the ferrules are not in very close alignment.
The present invention provides a method of fabricating the holding devices in a manner which ensures substantially exact axial alignment of the split sleeves in such devices.
A pair of ferrules having outside diameters corresponding to those of the ferrules to be held by the device are provided. Although the diameters of the two ferrules may be the same, the present invention will be shown and described in an embodiment wherein the ferrules have different outside diameters. The ferrules have the usual, central passageway, but no optical fiber is positioned therein. Rather, a gauge in the form of an elongated wire or filament having a diameter equal to the diameters of the ferrule passageways (which are equal to one another) is inserted through the passageway of both ferrules, thus placing the ferrules in precise axial alignment. Split sleeves which have inside diameters approximately equal to or slightly smaller than the outside diameters of the ferrules are then installed on and frictionally engage the ferrules. The ferrules have axial lengths in excess of the axial lengths of the sleeves, whereby, when the ferrules have one end positioned flush with the opposing ends of the sleeves, the outer ends of the ferrules extend past the outer ends of the sleeves. Because the ferrules are carefully checked to ensure that they conform to tight tolerances both as to outside and inside diameter and to concentricity, the axes of the two split sleeves engaging the ferrules are necessarily in essentially exact alignment.
In a first embodiment of the invention, a mold having a central cavity is prepared, preferably in three sections, a top, a central body and a bottom. The central body section includes a cavity having a central axis and a larger radial cross section than the split sleeves. The cavity is preferably circular in radial cross section, either of uniform diameter or of two or more different diameters throughout its length. The top and bottom sections each include a cylindrical cavity extending into the side which mates with the body section and having a diameter substantially equal to that of a respective ferrule and a depth equal to the axial length of portion of the ferrule which extends from the split sleeve. The axial length of the body section is substantially equal to the axial distance between the outer ends of the split sleeves. Thus, when the assembly consisting of the two ferrules, the two split sleeves and the elongated gauge is placed within the cavity of the body section, the ends of the two ferrules project from opposite ends of the body for distances equal to the depths of the cylindrical cavities in the top and bottom mold sections.
The three sections are assembled by inserting the outer ends of the ferrules into the respective cavities of the top and bottom sections, which are aligned with the central axis of the body section. The split sleeves are suspended within the cavity of the body section in spaced relation to the walls thereof. A suitable plastic or other potting agent in flowable form is then injected into the die cavity of the central section, surrounding the split sleeves. When the potting agent hardens, the top and bottom mold sections are removed and the molded article is removed from the center section cavity. The ferrules and gauge are withdrawn, leaving the split sleeves within the molded body in precisely coaxial relation. The holding device is then ready for use with optical fiber connectors having ferrules with outer diameters corresponding to the inner diameters of the split sleeves of the device.
In a second embodiment, the ferrules, split sleeves and gauge are mutually assembled in the same manner as in the first embodiment. The split sleeves are then coated with a quick drying epoxy and inserted into a stainless steel cylinder having an inside diameter a few thousandths of an inch less than the outside diameter of the largest of the split sleeves. Sufficient epoxy is applied to ensure that the space between the inside surface of the cylinder and the outside surface of the sleeves is substantially filled with epoxy. When the epoxy has dried (solidified) the gauge is removed from the ferrules and the ferrules are removed from the sleeves, leaving the sleeves permanently encased in the cylinder in essentially exact axial alignment.
The foregoing and other features of the invention will be more readily understood and fully appreciated from the following detailed description, taken in conjunction with the accompanying drawings.